try this: at least a couple of times/day, tighten that darn sphincter as if you were trying to shut off a bowel movement. hold it for a few seconds. in other words, exercise it to strengthen it. get it in shape/tone. I had a different problem with my sphincter: every once in awhile, after intercourse, it would spasm---come on real slow and then become a painful dull ache which would last several minutes. Ever since I employed the exercise routine, the problem has not resurfaced. let me know if this helps.
Most probably it is anal fissure cureable with Diltiazem ointment.
I had a similar problem. Grumpy56 s suggestion: tightening the sphincter muscles a few seconds for a few times a day helps. I find that problem is caused in my case by sitting too long on the toilet. I dislike public toilets and spend enough time in loo at home in the mornings till I feel my bowels are empty. But the age (I mean getting older) and type of food consumed effect bowel function. Apparently the healthy style of pooping is 'dump and go'. Less time in loo and tightening exercise couple of times helped me to overcome the condition.
Scarlet290 did you find out what it is? I have the same symptoms.
It is a Magnesium deficiency
http://analfissure.editboard.com/t3296-anal-spasms-due-to-magnesium-deficiency
if you bite your nails, you could have pinworms. they don't really hurt anything, but you don't want them, either! if you engage in anal sex, it could be anal warts that are causing it. or if you have diabetes, it could be a fungal infection which is sometimes one of the first symptoms of the disease. or it could be caused by an allergic reaction to toilet paper or something you ate....rarely it can be a sign of an abscess, polyp or STD. best to go to your dr and let them have a look. i know it's embarrasing, but better to know than not! hope it's nothing serious and this helps you a little!
elizabeth